A new approach to battery design developed by researchers at MIT could provide a lightweight and inexpensive alternative to existing batteries for electric vehicles and the power grid. It could even make rejuvenating the battery as easy as pumping petrol into a car. The work, which was carried under the guidance of materials science professors W. Craig Carter and Yet-Ming Chiang, is described in a paper published recently in Advanced Energy Materials.
The new battery uses an innovative device called a semi-solid flow cell, in which solid particles suspended in an electrolyte are pumped through the system. These suspend particles form the active, positive and negative electrodes of the battery. They are separated by a filter, such as a thin porous membrane. A key feature of the new design is that separates the energy storage and energy discharge functions into separate physical structures. According to Chiang, this allows the battery to be designed more efficiently.
The new design should make it possible to reduce the size and cost of a complete battery system, including all of its structural support and connectors, to about half the current levels. Another potential advantage is that in vehicle applications, the battery could be rejuvenated by pumping out the used slurry and replacing with a fresh, fully charged slurry, while retaining the option of conventional recharging when time permits.
Although flow batteries are not new, existing designs use liquids with very low energy density, so they take up much more space than fuel cells and require rapid pumping of the fluid, further reducing efficiency. The new semi-solid flow batteries pioneered by Chiang and colleagues provide a tenfold improvement in energy density, along with lower manufacturing cost than conventional lithium-ion batteries. The higher energy density allows the flow rate to be reduced to a slow oozing motion.
Image: Dominick Reuter / MIT